/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/********************************************************************************
 * libc/pthread/pthread_barrierwait.c
 *
 *   Copyright (C) 2007, 2009, 2014 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ********************************************************************************/

/********************************************************************************
 * Included Files
 ********************************************************************************/

#include <tinyara/config.h>

#include <sys/types.h>
#include <pthread.h>
#include <semaphore.h>
#include <sched.h>
#include <errno.h>
#include <debug.h>

/********************************************************************************
 * Definitions
 ********************************************************************************/

/********************************************************************************
 * Private Type Declarations
 ********************************************************************************/

/********************************************************************************
 * Global Variables
 ********************************************************************************/

/********************************************************************************
 * Private Variables
 ********************************************************************************/

/********************************************************************************
 * Private Function Prototypes
 ********************************************************************************/

/********************************************************************************
 * Public Functions
 ********************************************************************************/

/********************************************************************************
 * Name: pthread_barrier_wait
 *
 * Description:
 *   The pthread_barrier_wait() function synchronizse participating threads at
 *   the barrier referenced by 'barrier'.  The calling thread is blocked until
 *   the required number of threads have called pthread_barrier_wait() specifying
 *   the same 'barrier'.  When the required number of threads have called
 *   pthread_barrier_wait() specifying the 'barrier', the constant
 *   PTHREAD_BARRIER_SERIAL_THREAD will be returned to one unspecified thread
 *   and zero will be returned to each of the remaining threads. At this point,
 *   the barrier will be reset to the state it had as a result of the most recent
 *   pthread_barrier_init() function that referenced it.
 *
 *   The constant PTHREAD_BARRIER_SERIAL_THREAD is defined in pthread.h and its
 *   value must be distinct from any other value returned by pthread_barrier_wait().
 *
 *   The results are undefined if this function is called with an uninitialized
 *   barrier.
 *
 *   If a signal is delivered to a thread blocked on a barrier, upon return from
 *   the signal handler the thread will resume waiting at the barrier if the barrier
 *   wait has not completed; otherwise, the thread will continue as normal from
 *   the completed barrier wait. Until the thread in the signal handler returns
 *   from it, it is unspecified whether other threads may proceed past the barrier
 *   once they have all reached it.
 *
 *   A thread that has blocked on a barrier will not prevent any unblocked thread
 *   that is eligible to use the same processing resources from eventually making
 *   forward progress in its execution.  Eligibility for processing resources will
 *   be determined by the scheduling policy.
 *
 * Parameters:
 *   barrier - the barrier to wait on
 *
 * Return Value:
 *   0 (OK) on success or EINVAL if the barrier is not valid.
 *
 * Assumptions:
 *
 ********************************************************************************/

int pthread_barrier_wait(FAR pthread_barrier_t *barrier)
{
	int semcount;
	int ret = OK;

	if (!barrier) {
		return EINVAL;
	}

	/* Disable pre-emption throughout the following */

	sched_lock();

	/* Find out how many threads are already waiting at the barrier */

	ret = sem_getvalue(&barrier->sem, &semcount);
	if (ret != OK) {
		sched_unlock();
		return EINVAL;
	}

	/* If the number of waiters would be equal to the count, then we are done */

	if ((1 - semcount) >= (int)barrier->count) {
		/* Free all of the waiting threads */

		while (semcount < 0) {
			(void)sem_post(&barrier->sem);
			(void)sem_getvalue(&barrier->sem, &semcount);
		}

		/* Then return PTHREAD_BARRIER_SERIAL_THREAD to the final thread */

		sched_unlock();
		return PTHREAD_BARRIER_SERIAL_THREAD;
	} else {
		/* Otherwise, this thread must wait as well */

		while (sem_wait(&barrier->sem) != OK) {
			/* If the thread is awakened by a signal, just continue to wait */

			int errornumber = get_errno();
			if (errornumber != EINTR) {
				/* If it is awakened by some other error, then there is a
				 * problem
				 */

				sched_unlock();
				return errornumber;
			}
		}

		/* We will only get here when we are one of the N-1 threads that were
		 * waiting for the final thread at the barrier.  We just need to return
		 * zero.
		 */

		sched_unlock();
		return 0;
	}
}
